The present invention relates generally to articulated vehicles, and more particularly to a split-frame vehicle which articulates by rotation about an axial rotator joint located between a front sub-frame and a rear sub-frame.
Articulated vehicles typically include an articulating joint located inboard to the vehicle providing flexibility about at least one axis. An articulating joint may permit rotation of a first frame member relative to a second frame member about an axis which is substantially parallel to the surface upon which the vehicle is being operated (Rotation). The articulating joint may also permit a pivoting motion of a first frame member relative to a second frame member about a second axis which is substantially perpendicular to the surface upon which the vehicle is being operated (Pivot). In many articulating vehicles, these two capabilities taken in combination permit articulated vehicles to travel in a manner which permits the respective frame members to roll and yaw relative to one another and the surface upon which the vehicle is being operated. In many instances the articulating vehicle""s capability to pivot a first frame member relative to a second frame member is the very feature which allows the vehicle to change direction during operation.
Conventional split-frame articulating vehicles are designed for off-road use. It would be advantageous if a split-frame vehicle were capable of operating in the articulating mode for off-road use and in a rigid/non-articulating mode like a conventional on-road vehicle for highway travel. It would also be advantageous to provide such a vehicle with rear steering that is not tied to the vehicles ability to pivot the frame members.
Accordingly, the invention is directed to a split-frame vehicle in which the front and rear sub-frames may rotate relative to one another along a longitudinal axis that runs generally parallel to the ground. The relative rotation of the sub-frames allows the front and rear axles to lie in different planes to help keep all four wheels on the ground in uneven terrain. The invention includes three basic novel features that may be incorporated alone or in combination into a vehicle frame assembly and a split-frame vehicle. The first feature is a locking mechanism operatively coupled between the front and rear sub-frames. The locking mechanism is operative between a locked position in which the sub-frames are rigidly coupled and an unlocked position in which the sub-frames are free to rotate relative to one another. This first feature makes it practical to use the vehicle both off-road in the unlocked xe2x80x9carticulatingxe2x80x9d mode and in the locked mode like a conventional on-road vehicle.
The second basic feature of the invention is an axial rotator joint connected between the sub-frames. The joint allows the sub-frames to rotate relative to one another along the longitudinal axis that runs generally parallel to the ground while, at the same time, providing a path for transferring driving power through the joint. The joint includes a first bearing plate connected to the front sub-frame and a second bearing plate connected to the second sub-frame. The faces of each bearing plate bear on one another and define the rotational interface between the sub-frames. A drive shaft extends through an opening in the center of each bearing plate. The bearing plates are oriented so that the face of each plate is perpendicular to the longitudinal axis that runs generally parallel to the ground and the drive shaft extends along this longitudinal axis. It is expected that, in most situations, the axial rotator joint will be located along the mid-line of the sub-frames and a suitable yoke will be attached to each end of the drive shaft for connection to the vehicle""s front and rear drive lines.
Rear steering is incorporated into a split-frame four-wheel drive vehicle as the third basic feature of the invention. This split-frame vehicle includes a front set of steerable wheels drivingly coupled to the transmission through a first drive train and a rear set of steerable wheels drivingly coupled to the transmission through a second drive train. The second drive train includes a front drive line and a rear drive line. An axial rotator joint, such as the one described above, couples the front sub-frame to the rear sub-frame and the drive shaft in the joint connects the front and rear drive lines so that power may be transmitted through the rotator joint from the engine to the rear wheels. The vehicle also includes a rear steering linkage connected to the rear wheels. In one preferred version of this vehicle, steering force is delivered to the rear wheels by a hydraulic cylinder connected to the rear steering linkage. A hydraulic pump powers the cylinder and a controller located in the cab of the vehicle controls the pump and, therefore, the direction movement of the rear wheels.
These and other novel features of the invention as summarized above and defined in the claims at the end of this Specification may be better understood with reference to the drawings and the following detailed description of the preferred embodiments of the invention.